Doping Sm3+ into ZnB2O4 phosphors and their structural and cathodoluminescence properties

Highlights: • ZnB₂O₄:Dy³⁺ phosphors were successfully prepared by low temperature chemical synthesis method. • The luminescence properties were studied by different excitation sources. • Phosphors exhibited reddish orange emission under electron beam excitation. • The critical distance and luminescence quenching were investigated. In this study, ZnB₂O₄:xSm³⁺ (0.01 ≤ x ≤ 0.05 mol) powder phosphors have been synthesized by low temperature chemical synthesis method. The structure and morphological observation of the phosphor samples were systematically monitored by X-ray powder diffraction (XRD) and environmental scanning electron microscope (ESEM) coupled to an energy dispersive X-ray spectrometer (EDS). The all diffraction peaks are well assigned to standard data card (PDF#39-1126). Emission properties of the samples were explored using light emission induced by an electron beam (i.e cathodoluminescence, CL) at room temperature (RT). When excited with electron beam, CL spectral measurements of scrutinized phosphors exhibit orange-red luminescence at 572 nm, 606 nm and 658 nm due to various transition from ground state to ⁶H_5/2,⁶H_7/2 and ⁴G_5/2 states, respectively. The transition ⁴G_5/2 → ⁶H_7/2 located at 606 nm can occur as hypersensitive transition having the selection rule ΔJ = ±1. The observed peaks are in the region of yellow reddish light of Sm³⁺. Experimental results verify that the optimum Sm³⁺ content in terms of intense luminescence for this series of phosphors was 2%. Beyond 2% of Sm³⁺ ions concentration, luminescence quenching occurs due to an enhanced probability of the energy transfer from one Sm³⁺ to another that matches in energy via cross-relaxation and dipole-dipole interactions according to Dexter theory. A suitable energy transfer model between two adjacent Sm³⁺ ions in the ZnB₂O₄ phosphors was accomplished by the electric dipole-dipole interaction. The critical transfer distance (R_c) for non-radiative energy transfer was found to be 21.52 Å at 2 mol % Sm³⁺ doped ZnB₂O₄. Additionally, thermoluminescence (TL) glow curves of undoped and Sm activated ZnB₂O₄ under beta irradiation of 10 Gy are also discussed here.